1. Field of the Invention
The present invention relates to an over-current protection device.
2. Description of the Related Art
Thermistors are used to protect circuits from being damaged by overheating or excessive current flowing through the circuits. A thermistor usually includes two electrodes and a resistance material disposed therebetween. The resistance material has low resistance when it is at room temperature, while when the temperature is raised to critical temperature or excessive current occurs in a circuit, the resistance increases several thousand times, prohibiting over-current to flow through the circuit so as to protect the circuit.
When the temperature is lowered back to room temperature or the over-current condition is no longer present in the circuit, the resistance of the thermistor returns to low resistance, allowing the circuit to operate normally. With such a reusable characteristic, thermistors are replacing fuses and are popularly used in high density electronic circuits.
However, conventional thermistors are not sufficiently sensitive to the variation of an electric field, so they cannot be used in applications, such as the protection of secondary batteries, that require protection devices to be activated at low temperature. Due to the need for protection devices that can be activated at low temperature to protect electronic devices, there is a need to improve upon the conventional thermistors.